PROJECT SUMMARY/ABSTRACT . Non-small cell lung cancer (NSCLC) and hepatocellular carcinoma (HCC) are leading cause of cancer death globally. Immune checkpoint inhibitors (CPIs), which block tumor immune-evasion signals and activate T-cell mediated antitumor immunity, have demonstrated clinical efficacy and are approved for several cancers including NSCLC and HCC. Despite this broad spectrum of activity, less than 50% of patients receive any sustained benefit from these compounds. Moreover the majority of patients who achieve a response will relapse within a year. There is an unmet clinical need for therapeutic approaches that overcome resistance and enhance efficacy of CPI therapies. Pharmacodynamics monitoring has been incorporated into clinical trials to define mechanisms of resistance to CPI therapy, indicating that tumors with low levels of immune infiltration, or `cold' tumors, tend to respond poorly to checkpoint inhibition. Oncolytic virotherapy uses engineered viruses to destroy tumor cells and promote antitumor immunity. Several oncolytic virotherapies have been evaluated clinically with the recent approval of an oncolytic Herpesvirus (T-VEC) to treat advanced melanoma. Vyriad is developing Vesicular stomatitis virus (VSV), a potent oncolytic virotherapy platform, as an intravenous therapy for advanced cancer. VSV-IFN?-NIS, an engineered recombinant VSV, has demonstrated potent preclinical efficacy and is currently being tested in a clinical trial for intravenous therapy of patients with advanced cancer. Preclinical studies demonstrate that VSV selectively amplifies in and kills tumor cells resulting in rapid and durable tumor remission following single-shot intravenous therapy in murine tumor models. Intravenous VSV therapy also elicits intratumoral CD8+ T-cell infiltration. The addition of PD-1/PD-L1 blockade extends duration of T-cell infiltration to significantly enhance tumor remission in a murine colorectal tumor model. These data indicate that oncolytic tumor destruction promotes influx of T-cells, while local immunosuppressive signals can be blocked by checkpoint inhibitors to promote activation and amplification of antitumor T-cell responses. These synergistic interactions have the potential to overcome both primary and acquired resistance to single- agent checkpoint inhibitor therapy. Our goal is to clinically advance the combination oncolytic viro- immunotherapy approach to treat patients with CPI refractory NSCLC and HCC. This goal is addressed in this SBIR Fast-track proposal by combining Vyriad's expertise in oncolytic virotherapy development with the world-class expertise of the Mayo Clinic Early Cancer Therapeutics Program. The proposed clinical study will provide critical feasibility and efficacy signals and indicate mode of action to support rapid advancement of this combination oncolytic viro-immunotherapy approach to treat CPI refractory cancer.